1. Field of the Invention
The present invention relates to a power source regenerative apparatus, and in particular, to a power source regenerative apparatus which regenerates induction electromotive force caused in decelerating a motor to a power source.
2. Description of the Related Art
In decelerating a motor, the motor is operated as a generator, thereby regenerative braking is executed. Such an apparatus for controlling the aforesaid regenerative braking has been generally known as a power source regenerative apparatus. According to a conventional power source regenerative apparatus, after a regenerative current of a certain interphase becomes zero, the regenerative current flows into the next interphase.
FIG. 10 is a time chart showing an on/off state of transistors of a conventional converter, showing a change for every time of transistors Tr1 through Tr6, which corresponds to a change of a supply voltage. (Incidentally, a circuit of the converter is as shown in FIG. 11.) In FIG. 10, transistors Tr1, Tr3 and Tr5 turn the phase indicative of the maximum potential in three-phase (R-phase, S-phase, T-phase) supply voltage to an on-state. On the other hand, transistors Tr2, Tr4 and Tr6 turn the phase indicative of the minimum potential in the aforesaid three-phase supply voltage to an on-state.
More specifically, the transistor Tr1 becomes an on-state in the case where the potential of R-phase is the maximum, and an off-state in other cases. Likewise, the transistors Tr3 and Tr5 become an on-state in the case where the potential of S-phase and T-phase is the maximum, and an off-state in other cases, respectively. Further, the transistor Tr2 becomes an on-state in the case where the potential of R-phase is the minimum, and an off-state in other cases. Likewise, the transistors Tr4 and Tr6 become an on-state in the case where the potential of S-phase and T-phase is the minimum, and an off-state in other cases, respectively.
For example, the potential of R-phase becomes the maximum; on the other hand, the potential of S-phase becomes the minimum, between time t102 and time t103. For this reason, the transistors Tr1 and Tr4 become an on-state, and other transistors become an off-state. Likewise, the potential of R-phase becomes the maximum; on the other hand, the potential of T-phase becomes the minimum, between time t103 and time t104. For this reason, the transistors Tr1 and Tr6 become an on-state, and other transistors become an off-state.
In this case, the minimum voltage changes from the S-phase to the T-phase at the time t103, so that the transistor Tr4 becomes an off-state while the transistor Tr6 becomes an on-state with a delay of a short time .DELTA.t from time t103. Such a switching of an on/off state in a transistor is executed at each of time t101, t102, . . . , t109.
FIGS. 11 through 13 are circuit diagrams showing the flow of a conventional regenerative current; FIG. 11 shows the flow of the regenerative current before the phase is switched, FIG. 12 shows the flow of the regenerative current when the phase is switched, and FIG. 13 shows the flow of the regenerative current after the phase is switched. In other words, FIGS. 11 through 13 show the flow of the regenerative current between time t102 and time t103 in FIG. 10, the flow of the regenerative current at time t103 in FIG. 10, and the flow of the regenerative current between time t103 and time t104 in FIG. 10, respectively.
First, the circuit configuration of the converter shown in FIGS. 11 through 13 will be explained below. The transistors Tr1 and Tr2 are connected in series with each other. More specifically, an emitter terminal of the transistor Tr1 and a collector terminal of the transistor Tr2 are connected with each other, and this junction point is connected to the R-phase of a power source 11 through an inductance. Likewise, an emitter terminal of the transistor Tr3 and a collector terminal of the transistor Tr4 are connected with each other, and this junction point is connected to the S-phase of the power source 11 through an inductance. An emitter terminal of the transistor Tr5 and a collector terminal of the transistor Tr6 are connected with each other, and this junction point is connected to the T-phase of the power source 11 through an inductance.
Transistors Tr1 and Tr2, Tr3 and Tr4, and Tr5 and Tr6, which are connected in series, are further connected in parallel. More specifically, collector terminals of the transistors Tr1, Tr3 and Tr5 are connected to each other, and a regenerative current limiting resistor R and a diode D are connected in parallel to the junction point. Likewise, emitter terminals of the transistors Tr2, Tr4 and Tr6 are connected with each other, and one terminal of a condenser C is connected in parallel to the junction point, as in the connection between the transistors Tr1 and Tr2, and the other terminal of the condenser C is connected to a junction point between one terminal of the aforesaid regenerative current limiting resistor R and a cathode terminal of the diode D.
In addition, a diode is connected in parallel to each of these transistors Tr1 through Tr6; for example, a cathode terminal of a diode D1 is connected to the collector terminal of the transistor Tr1, and an anode terminal thereof is connected to the emitter terminal of the transistor Tr1. Likewise, diodes D2, D3, D4, D5 and D6 are connected in parallel to the transistors Tr2, Tr3, Tr4, Tr5 and Tr6, respectively.
Next, the flow of the regenerative current at each time will be explained below.
First, a current by induction electromotive force caused in decelerating the motor (not shown) flows into both terminals of the aforesaid condenser C; for this reason, the potential of both terminals of the condenser C rises up. At that moment, the potential of one phase indicative of the maximum potential in three-phase supply voltages supplied from the power source 11 becomes lower than that of one terminal of the condenser C, and the potential of one phase indicative of the minimum potential in three-phase supply voltages supplied from the power source 11 becomes higher than that of the other terminal of the condenser C. As a result, a potential difference occurs between the supplied three-phase supply voltage and the condenser C. Further, transistors are turned ON, thereby Generating a regenerative current flowing into the power source 11 from the condenser C. The regenerative current Generated by the aforesaid phenomenon is hereinafter referred to as "regenerative current in decelerating."
In FIG. 11, the regenerative current in decelerating flows into the power source 11 as a phase current IR through the regenerative current limiting resistor R and the transistor Tr1. In this case, the potential of the T-phase is V.sub.T. Further, the regenerative current in decelerating flows into the condenser C as a phase current IS through the transistor Tr4 because the potential V.sub.S of the S-phase is lower than the potential V.sub.T of the T-phase, and the transistor Tr4 is turned on.
In FIG. 12, when a counter electromotive voltage occurs in an input inductance L by turning the transistor Tr4 off, the regenerative current in decelerating flows into the power source through the transistor Tr1 and the diode D3.
In FIG. 13, the regenerative current in decelerating flows into the power source 11 as the phase current IR through the regenerative current limiting resistor R and the transistor Tr1. Further, the regenerative current in decelerating flows into the motor (not shown) as the phase current IT through the transistor Tr6 because the potential V.sub.T of the T-phase is lower than the potential V.sub.S of the S-phase, and the transistor Tr6 is turned on.
Next, the flow of the regenerative current in switching the phase, shown in FIG. 12, will be explained below.
FIG. 14 is a circuit diagram showing the conventional flow of the regenerative current in switching the phase. In the figure, an inductance L1 denotes inductance of the power source, and an inductance L2 denotes inductance of the converter. Each of potentials VR1, VS1 and VT1 denote a potential of supply voltage, and each of potentials VR2, VS2 and VT2 denote a potential of other apparatuses connected to the power source. Incidentally, the same number is given to the same element as that shown in FIG. 12, and an explanation of the same element is omitted.
The regenerative current in decelerating flows into the transistor Tr1 as a fly-wheel current IR, IS caused by counter electromotive force of inductances L1.sub.S and L2.sub.S, through the diode D3.
For this reason, the potentials V.sub.R and V.sub.S are in a short-circuited state, and they become almost the same potential, so that each of them becomes an intermediate potential between the potentials VR1 and VS1. As a result, the potential VR2 becomes a potential in which a partial pressure is applied to the potentials VR1 and V.sub.R by using inductances L1.sub.R and L2.sub.R, and the potential VS2 becomes a potential in which a partial pressure is applied to the potentials VS1 and V.sub.S by using inductances L1.sub.S and L2.sub.S. Therefore, the interphase voltage of potentials VR2 and VS2 becomes lower than the original potential, so that a waveform of the power source is distorted.
FIG. 15 is a time chart of the conventional regenerative current, showing a change of interphase voltage and phase currents IT, IR and IS, which corresponds to a change of the supply voltage.
Distortion of the interphase voltage shown in FIG. 14 appears at each time t151, t152, . . . , t159 when the phase currents IT, IR and IS decrease. Further, the magnitude of distortion of the interphase voltage varies in accordance with a ratio of inductances L1 and L2.
For this reason, according to the conventional power source regenerative apparatus, there is a problem in that interference occurs in various apparatuses which are connected to a power source having distortion caused by regeneration as described above and which use a three-phase timing. In addition, there is a problem in that higher harmonics occur in the power source.